[PSUBS-MAILIST] Double Seal?

[hank pronk]

If you double up the O-rings you increase the pressure it takes to open the valve.  If I have it right, you want to put a second o-ring beside the original o-ring.  The design is flawed from the start.  Doubling the O-rings makes it worse.  The original valve if I recall takes 20% more internal pressure than external pressure to open, not including  any spring tension.   

Hank

From: James Frankland <jamesf at guernseysubmarine.com>
To: "personal_submersibles at psubs.org" <personal_submersibles at psubs.org> 
Sent: Wednesday, July 24, 2013 9:51:24 AM
Subject: [PSUBS-MAILIST] Double Seal?



Hi All,
 
I have to re-machine the pop off top of my overpressure valve.  I threaded the hole by hand and now i have finally attepted to fit it with its O ring, i can see that the bolt is not straight, causing mis-seating of the valve top.   Im not over happy with having the bolt passing through anyway as it doesnt slide very easily.  

So, im going to machine up a new smooth shaft which should be straight.  Thats easy enough.
 
BUT, at the same time, i am tempted to put in a second O ring groove and have 2 O rings on the pop off top.  There is enough room for one outside the existing.  

I seem to remember there was discussion on double O rings a while ago.  Anyone have any thoughts on this idea?  Seems to me to be a good idea as its got 2 seals, but ?
 
Pic here as i was machining it.
 
Kind Regards
James
 
http://www.guernseysubmarine.com/publication2_files/Page20544.htm
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